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Old 09-25-2019, 08:47 PM   #1
Opposed_forces
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Default Wrx with sohc heads ej255/251

For starters Iíll say I did search and didnít find any definitive answers, I found similar questions and the only answers were go search. Back story: I have a 2004 Saab 92-x turbo with a bad engine (I will call it a wrx from now on). I plan on putting an engine in the car for a few months and then transplanting it into my 1966 vw bug. The Saab will just be used to dial in the car and make sure it runs good. I have an ej255 short block and I want to put sohc heads in it and run it with the stock wrx harness and pcm. Ideally Iíd like to use 251 heads because I have a rebuilt set. I know the heads will physically fit and the turbo will have some clearance issues that can be worked out. I know I will need to plumb oil and coolant to the turbo. What Iím not sure about is ignition coils and camshaft gears. The wrx uses Coil on plugs and the 251/253 heads use conventional wires. Does subaru make a coil on plug coil from a later model sohc engine that I can fit on a 251 head and be compatible with the wrx harness? I can tig a bung to bolt down the coil if needed. Will the camshaft sensor read the sohc cam gear properly? Also if anyone has done a similar conversion Iíd love some feedback.
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Old 09-26-2019, 12:59 AM   #2
vicious_fishes
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2003 SOHC destroker

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nope, won't happen. all kind of sensor/ecu problems. you can swap shortblocks between cars but not heads.

check out rs25.com for a wealth of guys that have done this.
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Old 09-26-2019, 06:59 AM   #3
Opposed_forces
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Can you elaborate on all kinds of sensor/ ECU problems? The only sensor that would be swapped/different is the camshaft sensor. I searched rs25 but most of the information is about putting a turbo wrx engine in a car that didnít come with a turbo. My car doesnít have avcs and neither would the heads id be pitting on. The coils and the cam gear are the only things that I can see causing an issue.
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Old 09-26-2019, 07:40 AM   #4
vicious_fishes
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yes, which changes everything. also depending on your model years you'd go from cable to fly by wire.

search dohc to sohc conversion on rs25.
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Old 09-26-2019, 06:19 PM   #5
Opposed_forces
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There is no information about converting a wrx engine with wrx ecm to use sohc heads. I-wire and outfront both said the cam sensor will read properly. Now I just need to figure out ignition coils. If anyone has done this conversion and has input I would greatly appreciate it. Thanks for the help so far.
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Old 09-27-2019, 08:56 AM   #6
Einimas
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It should be possible to run sohc, coil with custom engine harness, with four diodes on signal side (bridging 1,2 via diode and 3,4 via diode).
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Old 10-13-2019, 05:37 AM   #7
Einimas
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If you are still going this way. Today I tried putting ej205 coil in ej201 and the boot doesnt even reach the plug, so go with sohc coil.
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